HD-SDI, 3G-SDI, 6G-SDI, 12G-SDI, 24G-SDI, 48G-SDI, Detailed Explanation of SDI Technology: From Basics to High-Speed Evolution

In the professional audio-visual transmission field, SDI (Serial Digital Interface) is definitely one of the core standards. It sends uncompressed digital audio and video signals in a serial way, boasting advantages like low latency, high stability, and strong anti-interference ability. You’ll find it widely used in scenarios such as TV stations, video production, security monitoring, and stage performances. Unlike HDMI and DisplayPort interfaces for home use, SDI is built specifically for professional needs. It supports long-distance transmission and doesn’t require complicated protocol conversion, which helps keep the original quality of audio and video as intact as possible. As audio-visual technology moves toward high definition (HD) and ultra-high definition (UHD), the SDI standard has also been updated continuously—from the initial standard definition (SD) version to high-speed versions that can handle 8K and even higher resolutions. Below, we’ll break down the core definition of SDI and the technical features of each generation of standards.

What is SDI?

SDI, short for Serial Digital Interface, is a collection of digital audio-visual transmission standards set by SMPTE (the Society of Motion Picture and Television Engineers). Its core idea is to convert parallel digital audio-visual data into serial data, which is then transmitted via media like coaxial cables or optical fibers. No signal compression is needed during transmission, so it can achieve distortion-free and low-latency audio-visual delivery. Besides video signals, SDI interfaces can also send embedded audio signals and control data at the same time. This greatly simplifies the wiring and connections of professional audio-visual systems. Compared with analog transmission, SDI signals are more resistant to interference and can travel farther. It’s the key technology that replaced analog interfaces in the professional audio-visual industry.

What is SD-SDI?

SD-SDI is the earliest SDI standard, corresponding to SMPTE 259M (released in 1989). It has a transmission rate of 270 Mbps, mainly used for sending standard definition digital audio-visual signals. It supports resolutions like 720×576 (PAL system) and 720×480 (NTSC system), with frame rates of 25fps or 30fps. SD-SDI uses BNC interfaces for physical connection, and the main transmission medium is 75Ω coaxial cables. It can transmit signals up to about 100 meters on ordinary coaxial cables. Before HD technology became popular, SD-SDI was widely used in SD TV stations, old security systems, and SD video production equipment—it was the mainstream standard for professional audio-visual transmission in the SD era. With the development of HD and UHD technology, SD-SDI has gradually faded from mainstream use, but it’s still found in some old devices and specific SD scenarios.

What is HD-SDI?

As HD audio-visual technology emerged, SD-SDI could no longer meet the needs of HD signal transmission. That’s when HD-SDI (High Definition SDI) came into being, corresponding to SMPTE 292M (released in 1998). Its transmission rate jumped to 1.485 Gbps (with an actual effective rate of about 1.4835 Gbps), designed specifically for HD digital audio-visual signals. It supports resolutions like 720p (1280×720) and 1080i (1920×1080), with a maximum frame rate of 60fps. HD-SDI also uses BNC interfaces and 75Ω coaxial cables, and can transmit up to about 100 meters on high-quality coaxial cables. The arrival of HD-SDI drove the development of HD broadcasting, HD video production, and HD monitoring. It became the core standard for professional audio-visual transmission in the HD era. Even today, with UHD technology widespread, HD-SDI is still commonly used in many HD scenarios and holds a high market share.

What is 3G-SDI?

While HD-SDI can handle HD signals, it can’t support 1080p (progressive scan) HD signals. To solve this problem, the 3G-SDI standard was launched, corresponding to SMPTE 424M (released in 2006). Its transmission rate is 3 Gbps (actual effective rate about 2.97 Gbps)—twice that of HD-SDI—allowing stable transmission of 1080p60 (1920×1080, 60fps progressive scan) HD audio-visual signals. 3G-SDI uses a single-link transmission method, which is much simpler than the traditional dual-link HD-SDI solution for wiring and device connections. It still uses BNC interfaces and 75Ω coaxial cables, with a transmission distance of about 100 meters. 3G-SDI is widely used in scenarios that require high image quality and frame rates, such as HD video production, HD live broadcasting, and high-end monitoring. It’s an important transitional standard connecting HD and UHD technologies.

What is 6G-SDI?

With the rise of 4K UHD technology, 3G-SDI could no longer meet 4K signal transmission needs. Thus, the 6G-SDI standard was introduced, corresponding to SMPTE ST 2082-1 (released in 2015, the first sub-standard in the SMPTE ST 2082 UHD SDI series). Its transmission rate is 6 Gbps (actual effective rate about 5.94 Gbps), supporting 4K UHD signal transmission—specifically 3840×2160 (4K) resolution with a maximum frame rate of 30fps (4K30). 6G-SDI uses a single-link transmission method and BNC interfaces, with 75Ω coaxial cables as the medium. On high-quality coaxial cables, it can transmit up to 70-100 meters (depending on cable quality). 6G-SDI is the entry-level standard for 4K UHD audio-visual transmission, mainly used in scenarios that need 4K resolution but not high frame rates, such as 4K monitoring and some basic 4K post-production work.

What is 12G-SDI?

To meet the demand for 4K60 (3840×2160, 60fps progressive scan) UHD signal transmission, the 12G-SDI standard was released. It follows the SMPTE ST 2082 framework, with the 12Gbps speed specification added in 2015. Its transmission rate is 12 Gbps (actual effective rate about 11.88 Gbps)—twice that of 6G-SDI—enabling stable single-link transmission of 4K60 UHD audio-visual signals. 12G-SDI solved the complexity of traditional multi-link transmission for 4K60 signals, greatly simplifying the design and deployment of 4K UHD systems. It still uses BNC interfaces and 75Ω coaxial cables, with a transmission distance of about 70 meters on high-quality low-loss coaxial cables. If optical fiber is used, the transmission distance can be further extended. Today, 12G-SDI has become the mainstream standard in scenarios like 4K UHD broadcasting, 4K video production, and high-end 4K monitoring.

What is 24G-SDI?

As 8K UHD technology developed rapidly, there was a need for a faster SDI standard. The 24G-SDI standard was thus created, corresponding to SMPTE ST 2082-3 (released in 2016, focusing on 24Gbps 8K signal transmission specifications). Its transmission rate is 24 Gbps (actual effective rate about 23.76 Gbps), supporting 8K UHD signal transmission—specifically 7680×4320 (8K) resolution with a maximum frame rate of 30fps (8K30). 24G-SDI uses a single-link transmission method and BNC interfaces, but it has higher requirements for the transmission medium—needing low-loss, high-bandwidth 75Ω coaxial cables. It can transmit up to 50-70 meters (depending on cable quality). 24G-SDI is a transitional standard for 8K UHD audio-visual transmission, mainly used in early 8K broadcasting tests and 8K video production, laying the groundwork for faster SDI standards later.

What is 48G-SDI?

To support 8K60 (7680×4320, 60fps progressive scan) UHD signal transmission, the 48G-SDI standard was launched, corresponding to SMPTE ST 2082-5 (released in 2019, specifying 48Gbps 8K60 signal transmission). Its transmission rate is as high as 48 Gbps (actual effective rate about 47.52 Gbps)—four times that of 12G-SDI—enabling stable single-link transmission of 8K60 UHD audio-visual signals. 48G-SDI has very high requirements for transmission media and interfaces, usually using special low-loss coaxial cables or optical fibers to ensure stable signal transmission. Currently, 48G-SDI is mainly used in high-end scenarios that demand top image quality and frame rates, such as high-end 8K broadcasting, 8K video production, and 8K live broadcasting of large events. It’s an important development direction for future UHD audio-visual transmission.

Comparison of Core Parameters of Each SDI Standard

Standard Name	SMPTE Standard & Release Year	Transmission Rate	Supported Resolution & Frame Rate	Typical Transmission Distance (75Ω Coaxial Cable)
SD-SDI	SMPTE 259M (1989)	270 Mbps	PAL 720×576/25fps, NTSC 720×480/30fps	About 100 meters
HD-SDI	SMPTE 292M (1998)	1.485 Gbps (about 1.4835 Gbps)	720p/60fps, 1080i/60fps	About 100 meters
3G-SDI	SMPTE 424M (2006)	3 Gbps (about 2.97 Gbps)	1080p/60fps	About 100 meters
6G-SDI	SMPTE ST 2082-1 (2015)	6 Gbps (about 5.94 Gbps)	4K (3840×2160)/30fps	70-100 meters (depends on cable quality)
12G-SDI	SMPTE ST 2082-1 (2015)	12 Gbps (about 11.88 Gbps)	4K (3840×2160)/60fps	About 70 meters (high-quality low-loss cable)
24G-SDI	SMPTE ST 2082-3 (2016)	24 Gbps (about 23.76 Gbps)	8K (7680×4320)/30fps	50-70 meters (low-loss high-bandwidth cable)
48G-SDI	SMPTE ST 2082-5 (2019)	48 Gbps (about 47.52 Gbps)	8K (7680×4320)/60fps	Requires special cable/fiber

Application of SDI Technology

Thanks to its core advantages—uncompressed transmission, low latency, high stability, and long-distance delivery—SDI technology has deeply penetrated many professional audio-visual fields, becoming a key support for high-quality signal transmission in various industries. Different SDI standards form clear application layers based on the resolution and frame rate requirements of different scenarios. Below are its four most core application areas:

1. Broadcast & TV Station

TV stations are a core application scenario for SDI technology. From early signal collection and post-production to studio live broadcasting and signal distribution, SDI standards are used throughout the process. In the SD era, SD-SDI handled the transmission of traditional TV programs. In the HD era, HD-SDI became the mainstream standard for news live broadcasts and regular program airings. With the popularity of UHD TV, 12G-SDI is now widely used in 4K studio construction and 4K program simulcasting (SD/HD/UHD). Meanwhile, 48G-SDI is gradually being adopted in high-end scenarios like 8K UHD channel launches and 8K live broadcasts of major sports events (such as the Olympic Games and World Cup). SDI’s low latency ensures no lag and strong synchronization during live broadcasts, while its anti-interference ability adapts to the complex wiring environment of TV stations, avoiding image quality loss during transmission.

2. Video Production Field

In the entire video production process—from shooting to post-production—SDI technology is key to ensuring lossless image quality transmission. During shooting, professional cameras are often equipped with 3G-SDI interfaces, which can send 1080p60 HD signals to monitors in real time, letting photographers check the footage instantly. For 4K video shooting, 12G-SDI interfaces are used to achieve lossless transmission of 4K60 signals. In post-production, non-linear editing systems, color grading tables, and oscilloscopes are connected via SDI interfaces, ensuring that original uncompressed footage retains its quality during editing, color grading, and special effects production. Additionally, in links like video compositing and master tape production, 6G-SDI, 24G-SDI, and 48G-SDI meet the needs of 4K30, 8K30, and 8K60 footage processing respectively, supporting UHD video production.

3. Security Monitoring

Security monitoring has very high requirements for real-time and stable signals. Thanks to its long-distance transmission advantage, SDI technology is an important choice for mid-to-high-end security systems. In regular monitoring scenarios like residential areas, shopping malls, and factories, HD-SDI (supporting 720p/1080i) and 3G-SDI (supporting 1080p60) can meet HD real-time monitoring needs, with a transmission distance of up to 100 meters. No complicated encoding or decoding is needed, avoiding latency and image quality loss caused by digital compression. In long-distance, large-scale monitoring scenarios such as urban security, highways, and border surveillance, SDI systems combined with optical fibers can transmit signals for several kilometers or even tens of kilometers, while supporting synchronous convergence of multi-camera signals. For 4K monitoring, 6G-SDI (4K30) and 12G-SDI (4K60) adapt to the signal transmission needs of UHD surveillance cameras, improving the ability to capture details in monitoring images.

4. Stage Performances & Live Event

In live broadcasts and stage displays of large events like concerts, press conferences, and sports matches, SDI technology is responsible for core tasks such as multi-camera signal switching, on-site large-screen display, and live signal backhaul. Event venues usually connect multiple camera signals and use SDI switchers for real-time image switching. HD-SDI and 3G-SDI can meet HD multi-camera live broadcast needs, while 12G-SDI supports 4K UHD on-site displays and live broadcasts. SDI’s low latency ensures no delay between the on-site large screen and the camera footage, enhancing the audience’s on-site experience. At the same time, SDI signals can be sent back to TV stations or live streaming platforms via optical fiber links, ensuring stable transmission. Additionally, in stage lighting and audio control systems, SDI can also transmit control signals simultaneously, simplifying system wiring.

Summary of SDI Standard Evolution

From SD-SDI to 48G-SDI, the evolution of SDI standards has always centered on the core needs of "higher transmission rate, higher resolution, and higher frame rate." Each new standard has driven technological innovation in the professional audio-visual field. From SD to HD, and then to 4K and 8K UHD, SDI standards have maintained a core position in professional audio-visual transmission thanks to their advantages of uncompressed transmission, low latency, and high stability. Their in-depth application in broadcasting, video production, monitoring, and stage performance further confirms their irreplaceable professional value. In the future, with the continuous development of audio-visual technology, SDI standards are likely to evolve toward higher speeds and broader bandwidth to meet the needs of emerging application scenarios such as virtual reality (VR), augmented reality (AR), and beyond-8K UHD.


Reference:
https://www.smpte.org/
https://en.wikipedia.org/wiki/Serial_digital_interface